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Biomedical subjects

D K Bewley

Publications and source records attributed to D K Bewley.

At least 37 records · Page 2Linked to original sources
PubMed1980

Neutron beams from protons on beryllium.

Measurements of dose rate and penetration in water have been made for neutron beams produced by 30--75 MeV protons on beryllium. The effects of Polythene filters added on the target side of the collimator have also been studied. A neutron beam comparable with a photon beam from a 4--8 MeV linear accelerator can be produced with p/Be neutrons plus 5 cm Polythene filtrations, with protons in the range 50--75 MeV. This is a more economical method than use of the d/Be reaction.

Beryllium↗
PubMed1980

Metabolic activity of sodium, measured by neutron activation, in the hands of patients suffering from bone diseases: concise communication.

Turnover of sodium in the human hand was studied by neutron activation. Patients suffering from various metabolic abnormalities affecting the skeleton, who were undergoing routine neutron activation for the measurement of calcium, were investigated along with a group of healthy volunteers. Neutron activation labels the sodium atoms simultaneously and with equal probability regardless of the turnover time of individual body compartments. The loss of sodium can be described either by a sum of two exponentials or by a single power function. Distinctions between patients and normal subjects were not apparent from the exponential model but were brought out by the power function. The exponent of time in the latter is a measure of clearance rate. The mean values of this parameter in (a) a group of patients suffering from acromegaly: (b) a group including Paget's disease, osteoporosis, Cushing's disease, and hyperparathyroidism; and (c) a group of healthy subjects, were found to be significantly different from each other.

Activation Analysis↗
PubMed1979

X-ray emission analysis of human plasma by proton excitation of thick samples in air.

Thick plasma samples have been irradiated in air by 2.3 MeV protons for trace elemental analysis by proton-induced X-ray emission spectroscopy. Accurate calibration curves were obtained for Fe, Zn and Sr and detection limits in dry plasma were estimated to be 0.08 PPM for Fe, 0.065 PPM for Zn and 0.12 PPM for Sr. Low temperature ashing of these samples improved the detection limits by a factor of 3 but reduced the precision and resulted in loss of bromine from the plasma. Mass absorption coefficients for low energy X-rays in dry plasma were measured and X-ray attenuation in the sample was found to prevent the detection of trace elements with Z less than 26. The method was used to determine Sr in plasma from a patient with bone disease, the Sr being a non-radioactive bone-seeking tracer element. The results, which were in the 3--13 PPM range, were in good general agreement with the analysis of the same samples by flame photometry.

Air↗
PubMed1978

The use of 10B to enhance the tumour dose in fast-neutron therapy.

Incorporation of 10B in tumours treated by fast-neutron therapy would increase the tumour dose via the reaction 10B(n, alpha)7Li which occurs with partially thermalised neutrons. The extent of the dose enhancement was measured for neutron beams with median energies of 2.4, 3.3, 7.0 and 9.0 MeV by two techniques: with a BF3 proportional counter in three beams and activation of 23Na in the fourth. The results obtained with the two techniques are in good agreement. The magnitude of the dose enhancement depends upon the depth, field size and neutron beam energy. The dose enhancement at a depth of 8 cm varied from 0.32% with the lowest-energy beam to 0.07% with the highest-energy beam for each microgram of 10B uptake per gram of tissue. The products of the reaction in 10B would, however, have an RBE about twice that of the fast-neutron dose in the absence of boron. The method may be useful if drugs providing adequate uptake of 10B can be synthesised.

Beryllium↗
PubMed1978

On the nature and significance of the radiation outside the beam in neutron therapy.

Measurements have been made of beam profiles at 10 cm deep for the neutron beam of mean energy 7.5 MeV produced by the MRC cyclotron at Hammersmith Hospital. Neutron and gamma-ray doses in water were measured with a tissue-equivalent chamber and a Geiger-Müller counter. Far outside the beam the radiation consists mostly of gamma rays penetrating the shielding. Perfect shielding would reduce this but the profile of biologically effective dose would still be worse than that from conventional X- and gamma-ray generators owing to the high RBE of small doses of neutrons. The main hazard to the patient is probably that of carcinogenesis. An approximate assessment is made of this hazard which is compared with that estimated in previous publications.

Gamma Rays↗
PubMed1976

A comparison for use in radiotherapy of neutron beams generated with 16 and 42 MeV deuterons on beryllium.

The physical and radiobiological properties of two neutron beams have been compared. The beams were generated by deuterons of 16 MeV at Hammersmith Hospital and 42 MeV at Harwell, in both cases falling on a Be/Cu target. The dose-rate and depth-dose characteristics at the higher energy were found to be superior to those at the lower energy. Collimation and shielding at the higher energy are facilitated by the greater degree of forward-peaking and by the fact that a higher dose-rate allows longer collimators to be used. Attenuation in iron was found to be similar at the two energies. The radiobiological properties of the two neutron beams are very similar. There is a difference of about 20 per cent in RBE for effects on mammalian tissues for doses between 300 and 2,000 rad of neutrons. The OER and the sparing effect of two large fractions are the same for the two beams.

Animals↗